FIGS. 12-14 are schematic assembled views of a secondary battery of the prior art, in which, FIG. 12 is a schematic view illustrating a connection relationship between tabs and electrode terminals before the tabs are bent in the secondary battery of the prior art; FIG. 13 is a perspective view of the secondary battery of the prior art; FIG. 14 is an enlarged view of a circle part of FIG. 13.
As shown in these figures, in the prior art, one end of each connecting piece 3 is welded to one tab 22, the other end of each connecting piece 3 is welded to one electrode terminal 11, and after each connecting piece 3 is welded to the tab 22 and the electrode terminal 11, there is a process of bending the tab, the tab 22 need be bent 180 degrees (that is, the tab 22 is bent twice to form a horizontal U-shape, as shown in FIG. 14), and at the same time each connecting piece 3 is also bent 180 degrees (to similarly form a horizontal U-shape), so that one of the connecting piece 3 and the tab 22 covers and clamps the other of the connecting piece 3 and the tab 22 relative to each other at a position where the connecting piece 3 and the tab 22 are welded together, therefore it has a high requirement on bending property of the connecting piece 3 and bending property of the tab 22. Because the connecting piece 3 easily generates fatigue crack and even fractures at bent positions, thereby affecting the life of the connecting piece 3. Moreover, after the tab 22 is bent twice, a part of the tab 22 far away from the connecting piece 3 (that is, the part where the tab 22 is connected to a main body 21 of the cell 2) is easily pulled during bending, which may result in that the tab 22 cracks and fractures at the part. In addition, because the connecting piece 3 is bent 180 degrees and the tab 22 is bent twice, the operation process is increased and the production cost is increased, the production efficiency is reduced, that both the connecting piece 3 and the tab 22 are bent on the main body 21 of the cell 2 in form of horizontal U-shape will take up more space, so that it is not beneficial to increase the energy density of the secondary battery.